Air gun

ABSTRACT

A firing mechanism for a compressed gas gun includes a heating chamber attached to a fluid source. Gas or liquified gas from the fluid source is admitted into the heating chamber through a valve, which seals the gas source from the heating chamber thereby preventing back flow of the gas from the heating chamber to the source. A heating element inside the heating chamber is then energized to heat the gas to a temperature and pressure to well above that of the gas source. When a predetermined temperature and pressure is achieved, the heating chamber is exhausted into the breech of the gas gun to expel the projectile.

BACKGROUND OF THE INVENTION

This invention relates generally to weapons and, in particular, to air rifles and other weapons capable of firing a projectile using a compressed gas source.

Air guns and other weapons capable of firing a pellet or other projectile using compressed gas rather than an exploding cartridge are well known. Also well known is that the available energy to propel the projectile is a function of both pressure and temperature of the gas charge. As with any expander in a conventional heat engine, heat energy added to the gas charge after compression serves to increase the work done as the gas expands and accelerates the projectile in the barrel. Regardless of the initial pressure of the charge, adding heat prior to, or during expansion will increase muzzle energy of the projectile. Thus, it can be seen that heat addition can be used to offset physical limitations in: pressure capability of the gun components, physical strength of the user in the case of pump type guns and, in the case of carbon dioxide, the available vapor pressure of a liquified gas at ambient temperature.

SUMMARY OF THE INVENTION

The present invention comprises a firing mechanism for a compressed gas gun. According to an illustrative embodiment, the firing mechanism comprises a heating chamber attached to a fluid source such as an air or gas pump, compressed gas canister or liquified gas canister. Gas or liquified gas from the gas source is admitted into the heating chamber through a valve, which can be a simple check valve that seals the gas source from the heating chamber, preventing back flow of the gas from the heating chamber to the source. A heating element inside the heating chamber is then electrically energized to heat the gas to a temperature and pressure to well above that of the gas source. When a desired temperature and/or pressure is achieved, the gas charge is exhausted into the breech of the gas gun to expel the projectile at a muzzle energy well above what could be achieved using gas compression alone.

BRIEF DESCRIPTION OF THE DRAWING

The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements and, in which:

FIG. 1 is the cross-sectional view of an air gun incorporating features of the present invention;

FIG. 2 is a close-up of a portion of the cross-sectional view of FIG. 1; and

FIG. 3 is a close-up of a portion of the cross-sectional view of FIG. 1.

DETAILED DESCRIPTION

The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and detailed description are not intended to limit the invention to the particular form disclosed, but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention.

With reference to the figures, and in particular FIGS. 1-2, an air gun 10 incorporating features of the present invention comprises a barrel 12 having a breech end 14 and a muzzle end (not shown). As used herein “air gun” means and refers to any rifle, mortar, howitzer, gun or any other device capable of expelling a projectile towards an intended target. Moreover, as used herein, the “breach” means and refers to any space on the side of a projectile opposite the open end of the gun barrel. Air gun 10 further comprises a main housing 16 which houses the heating group 18, shown in greater detail in FIG. 2. Main housing 16 also houses the trigger group 20, shown in greater detail in FIG. 3.

With particular reference to FIG. 2, the heating group 18 includes a pressure fitting 22 which is adapted to receive a source of a working fluid, for example from a conventional carbon dioxide canister, high pressure gas cylinder, hand operated air pump or electric air pump. As used herein, “gas” and “fluid” are used interchangeably and may refer to either a liquid or a gaseous substance, including but not limited to liquid carbon dioxide, gaseous carbon dioxide, water and air. Heating group 18 further comprises an inlet valve 24, which may be a check valve consisting of a valve chamber 32 containing check ball 26, a valve seat 28 and a bias spring 30. Check ball 26 may be made of any suitable material including stainless steel, or plain carbon steel, but is preferably a lightweight ceramic material to minimize the response time of valve 24. Although in the illustrative embodiment, inlet valve 24 comprises a check valve, other valves such as a solenoid valve, poppet valve or the like may be utilized without departing from the scope of the invention. Valve chamber 32 is interconnected with heating chamber 34 by way of a metering orifice 36 formed in metering orifice body 38. The operation of metering orifice 36 will be described more fully hereinafter.

A heating element 40 is disposed in heating chamber 34. Electrical contact is made between heating element 40 and an external power source which could be a lithium polymer or other high energy density battery (not shown) by means of an electrode 42 and the terminal 44 of heating element 40. The opposite end of the filament is retained in filament housing 122 by a screw. Electrical contact is through filament housing 122 and main housing 16 itself. A contact spring 46 contained within contact spring housing 116 maintains contact pressure between electrode 42 and terminal 44 while enabling heating element 42 to be readily replaceable. Electrode 42 is secured to main housing 16 by a feed through housing 48 which supports a high temperature, high pressure insulator 50. Heating element 40 may be made of any suitable high temperature material such as nickel chromium, FeCrAl, FeCrAlY, or other alloys having high strength at high temperature, but in the illustrative embodiment electrode 42 comprises Kanthal APM® alloy made by Sandvik. Alternatively, the fluid in heating chamber 34 may be heated using a metal-coated ceramic heating element, light emitting diode, semiconductor spark plug or conventional spark plug. The advantage of a semiconductor spark generator is ability to generate a high energy plasma with lower voltage than is needed to jump an air gap typical of a conventional spark plug. The heating element may be operated with or without closed-loop control of temperature.

Heating chamber 34 additionally includes an aperture 52 which is sealed by a window 54, which in the illustrative embodiment is made from fused quartz or borosilicate glass. Fused quartz and borosilicate glass are suitable for this application because of their optical clarity and resistance to high pressure although other optical materials may be advantageously employed without departing from the scope of the invention. A light sensor 58, which in the illustrative embodiment comprises a Kattni E315391 lux sensor is mounted at the output end 56 of window 54 so as to be able to detect the light emission, and therefore the temperature of, heating element 40. Alternatively, the light sensing circuit could be placed inside heating chamber 34, or a thermocouple, resistance monitor or other method could also be used to monitor the temperature of heating element 40 without departing from the scope of the invention. Heating chamber 34 includes a second aperture 60 which permits fluid communication between heating chamber 34 and a pressure sensor or transducer 62.

With additional reference to FIG. 3, trigger group 20 includes a discharge valve assembly 64 which seals the end 66 of heating chamber 34 opposite that of inlet valve 24. Discharge valve assembly 64 includes a main poppet valve 68 and a main valve seat 70 as well as a pilot valve 72. Main poppet valve 68 is biased against main valve seat 70 by main valve spring 74 which is disposed between the valve body 76 and balance piston 78 which is threaded onto the stem portion 80 of main poppet valve 68. Pilot valve 72 is biased against its seat 82 by pilot valve spring 84 which is disposed between balance piston 78 and a keeper 86 which is threaded onto the end portion 88 of pilot valve 72. A hammer lever 90 is mounted for rotation about hammer lever axle 92 and presses against the end portion 88 of pilot valve 72 via firing pin 94. Although hammer lever 90 may be manually operated, in the illustrative embodiment, hammer lever 90 is actuated by an electromagnetic coil 96 which operates on a solenoid plunger 98 which pulls solenoid plunger 98 toward hammer lever 90 until hammer pin 100 strikes hammer lever 90. In the illustrative embodiment, there is a gap “g” between hammer pin 100 and hammer lever 90. This lets the solenoid plunger 98 accelerate to a predetermined velocity prior to striking hammer lever 90, thereby allowing the inertia of solenoid plunger 98 to augment the force of the electromagnetic coil 96 to move hammer lever 90. This reduces the size and electrical requirements of electromagnetic coil 96. Furthermore, it can be seen in the illustrative embodiment that hammer lever 90 provides mechanical advantage between hammer pin 100 and firing pin 94 further reducing the size and electrical requirements of electromagnetic coil 96. A stop screw 102 may be employed to limit the travel of hammer lever 90.

The principal components of air gun 10 having been described, their operation will now be explained: A working fluid such as carbon dioxide from container 104 enters through pressure fitting 22 at a pressure sufficient to open inlet valve 24. The fluid then passes through metering orifice 36 past electrode 42 and into heating chamber 34. When the pressure in heating chamber 34 reaches a predetermined level approximately equal to the pressure upstream of inlet valve 24, inlet valve 24 closes, thereby sealing heating chamber 34 from container 104. According to the illustrative embodiment, once inlet valve 24 closes, electrical power is fed to heating element 40, which heats the working fluid in heating chamber 34 until a predetermined pressure and temperature is reached. (It should be noted that carbon dioxide becomes liquid above about 55 Bar pressure at room temperature and therefore this is a practical limitation of the available muzzle energy of a prior art carbon dioxide powered air gun. Heating the fixed mass of carbon dioxide in heating chamber 34 at pressure of 55 bar from room temperature (20 C) to 800 C, increases pressure to more than 380 Bar. The resultant energy addition is more than 650 Joules.)

Powering the heating element can be done manually by actuating a switch or by electronic means where power to the heating element is controlled or timed to prevent melting or burning of the element. In the illustrative embodiment, monitoring and control of the temperature of the heating element is accomplished by means of the light sensor 58 viewing the heating element 40 through window 54. The light sensor 58 provides feedback to the power circuit which controls the intensity of light from the element and thus the temperature of the element. A simple version of the algorithm is to simply turn off power to the element when light reaches a threshold intensity. Without power, heat leaves the element and at a designated lower threshold, the power is switched back on. In a more complex algorithm, the light sensor would provide an analog output based on intensity or electromagnetic frequency of the emission. Power to the element would be modulated in analog fashion or pulse-width modulated to hold a substantially constant emission level. Pressure is monitored via the pressure transducer 62. An audible or other signal alerts the user, or the gun automatically fires, when the chamber pressure is at the desired level.

Alternatively, the working fluid may be carried and dispensed as a liquid. Carbon dioxide for example, can be carried aboard the gun in a cannister in liquid form where its high density will increase the available shots per cannister fill. Liquid carbon dioxide has a density of approximately 773 kg per cubic meter at 57 Bar at room temperature (20 C). Air at 20 C and a pressure commensurate with high performance guns (300 Bar) has a density of 322 kg per cubic meter. Thus, for a given available cannister volume on the gun, mass of the propellant is more than doubled. Furthermore, a cannister and valving with the capability of handling 300 Bar pressure is significantly heavier and potentially more dangerous than that designed for the (roughly) 55 to 59 Bar pressure of carbon dioxide at room temperature.

If the carbon dioxide is introduced into the heating chamber in liquid form, it can be metered using a solenoid driven pintle (similar to an automobile fuel injector), sleeve or poppet valve or other type of high-speed short duration valve to accurately admit a specific amount of liquid in order to accurately set the muzzle energy of the projectile. The gun can feature two solenoid-actuated valves that are actuated in rapid succession and accurately timed such that the liquid admitted into the heating chamber by the first solenoid valve has time to flash to vapor in the chamber and be heated to the intended temperature before the second solenoid valve releases it into the breech of the barrel. For a given desired muzzle velocity, this arrangement allows accurate setting of the mass of the charge and the amount of heat applied to that mass in order to make most efficient use of the pressure and heat. An electronic controller would have preprogrammed algorithms that would set timing of the two solenoid valves based on input from the user. Considerable cooling effect is realized by the flashing of liquid to vapor in the chamber at each firing. This serves to increase charge mass, maintain consistency of conditions prior to heating and keep the surrounding parts cool.

Regardless of the working fluid, in order to fire the gun, electromagnetic coil 96 is activated which pulls solenoid plunger 98 inward until hammer pin 100 strikes hammer lever 90. As noted herein before, gap “g” permits solenoid plunger core 98 to accelerate to a desired velocity and therefore have a desired kinetic energy prior to hammer pin 100 striking hammer lever 90 thus augmenting the force of electromagnetic coil as hammer pin 100 strikes hammer lever 90. Hammer lever 90 then presses against firing pin 94, which in turn presses against the end portion 88 of pilot valve 72 opening pilot valve 72. Once pilot valve 72 is open high-pressure working fluid in heating chamber 34 passes through channel 106 and into balance piston chamber 108. The diameter of balance piston 78 being greater than the diameter of main valve seat 70, ensures that the net force is sufficient to move balance piston 78 and lift main poppet valve 68 off of valve seat 70. This action exhausts the gas charge in heating chamber 34 through main exhaust port 110 while at the same time the lateral motion of main poppet valve 68 allows pilot valve 72 to close thereby sealing off channel 106. The high-pressure working fluid exhausting through main exhaust port 110 is then channeled into the breech end 14 of barrel 12 to propel projectile 120. Residual pressure in balance piston chamber 108 is vented through balance piston exhaust port 112 and then out port 121 when lateral movement of the balance piston allows balance piston seal 118 to cross over port 112 and expose the balance piston chamber 108 to exhaust port 112. Pressure reduction in balance piston chamber 108 allows main valve spring 74, assisted by remaining pressure in the heating chamber, to return balance piston 78 and main poppet valve 68 to their initial positions.

It should be noted that as soon as projectile 120 exits barrel 12, the pressure in heating chamber 34 will drop rapidly as the chamber is essentially opened to the atmosphere. This would potentially allow the working fluid in container 104 to vent into the atmosphere and be wasted. Metering orifice 36 prevents excessive loss of working fluid from container 104 under these conditions by limiting the rate at which fluid can flow into heating chamber 34. It should also be noted that given the high pressures and temperatures involved, main poppet valve 68 and pilot valve 72 are preferably made of a metallic or ceramic material that withstands valve erosion, for example hardened and/or stainless steel or silicon nitride. Given that metal-to-metal seals or ceramic seals designed to operate at high temperatures may eventually wear, erode or inadequately seal at lower pressures, an auxiliary shut-off valve 114, which may be manual or automatic, is provided to seal container 104 during periods of storage. Auxiliary shut-off valve 114 may be a hermetic valve and is preferably located remotely from the heated components of air gun 10.

Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the invention. Accordingly, it is intended that the invention should be limited only to the extent required by the appended claims and the rules and principles of applicable law. Additionally, as used herein, references to direction such as “up” or “down” as well as recited materials or methods of attachment are intended to be exemplary and are not considered as limiting the invention and, unless otherwise specifically defined, the terms “generally,” “substantially,” or “approximately” when used with mathematical concepts or measurements mean within ±10 degrees of angle or within 10 percent of the measurement, whichever is greater. As used herein, a step of “providing” a structural element recited in a method claim means and includes obtaining, fabricating, purchasing, acquiring or otherwise gaining access to the structural element for performing the steps of the method. As used herein, the claim terms are to be given their broadest reasonable meaning unless a clear disavowal of that meaning appears in the record in substantially the following form (“As used herein the term ______ is defined to mean ______”) 

What is claimed is:
 1. A firing mechanism for a gun having a gun barrel, the gun barrel having a breech end and a muzzle end, the firing mechanism comprising: a heating chamber having an inlet and an outlet, the outlet operatively attached to the breech end of the gun barrel; a source of working fluid operatively attached to the inlet of the heating chamber; a heating element disposed within the heating chamber for heating a working fluid within the chamber; and a discharge valve operatively disposed in the outlet, the discharge valve being operable by a user to release the working fluid from the heating chamber into the breech end of the gun barrel.
 2. The firing mechanism of claim 1, further comprising: an inlet valve disposed in the inlet of the heating chamber, the inlet valve being operable to seal the heating chamber from the source of working fluid at a predetermined pressure, whereby pressure in the heating chamber can exceed pressure in the source without bleeding heated fluid back to the source.
 3. The firing mechanism of claim 1, further comprising: a sensor for determining a temperature of the heating element.
 4. The firing mechanism of claim 3, wherein: the sensor comprises a lux sensor optically coupled to the heating element.
 5. The firing mechanism of claim 1, wherein: the discharge valve comprises a main poppet valve in combination with a pilot valve, the main poppet valve having a first valve head and a first valve seat,
 6. The firing mechanism of claim 5, wherein: the pilot valve comprises a poppet valve having a second valve head that is smaller than the first valve head.
 7. The firing mechanism of claim 5, wherein: the pilot valve is coaxial with the main poppet valve.
 8. The firing mechanism of claim 5, further comprising: a balance piston disposed within a balance piston chamber, the balance piston having a diameter that is greater than a diameter of the first valve seat, the balance piston operably attached to the main poppet valve to open the main poppet valve when the pilot valve opens admitting pressure into the balance piston chamber.
 9. The firing mechanism of claim 1, wherein: the source of working fluid is a hand-operated pump.
 10. The firing mechanism of claim 1, wherein: the working fluid is liquid carbon dioxide.
 11. The firing mechanism of claim 1, wherein: the heating element comprises an electric heating element.
 12. The firing mechanism of claim 1, wherein the inlet valve has a flow area, the firing mechanism further comprising: an orifice operably disposed between the inlet valve and the heating chamber for controlling a rate at which fluid flows into the heating chamber, the orifice having a flow area less than that of the inlet valve. 